1. Field of the Invention
The field of art to which this invention pertains includes that of machine elements and mechanisms; more specifically, limited slip differential gearing having a negligible bias under light load conditions.
2. Description of the Prior Art
Heavy duty automotive-type differentials generally include a differential carrier that supports a ring gear which in turn is driven by a driving pinion powered by a drive shaft. Differential side gears are located in the housing, one side gear being connected to the inner end of one axle shaft and the other side gear being connected to the inner end of the other axle shaft. Multiple differential pinions are generally rotatably journaled on a cross carried by the differential housing, with the pinions being in meshing engagement with the side gears.
During the normal operation of such a differential mechanism, the end thrust on the side gears is directly proportional to the torque on the ring gear. Such end thrust on the side gears is in an axial or longitudinally outward direction, that is, away from the differential and toward the axle ends. To provide a torque proportioning differential, i.e., to restrict the differential action so that one wheel will not spin if it loses traction, it is well known in the art to use clutches between the carrier (on which the ring gear is mounted) and the respective side gears. It will be appreciated that the meshing of the pinion gears with the side gears causes the previously-mentioned end thrust. The result of such end thrust is to apply the clutches and thus restrict the differential action of the mechanism. Thus, these clutches restrict the difference in speed between the two axle shafts that are connected to the side gears, which difference in speed occurs during turning operations.
One known limited slip differential of the type previously discussed has a constant bias of approximately 2.0, which means that the torque on one axle shaft can be 2 times the torque on the other shaft. This high bias, which is necessary to prevent tire slippage in many applications under many operating conditions, however, is not necessary in some other operating conditions. For instance, a logging truck requires a high bias while "access logging" when on a side grade with weight transferred to the inside tires. However, this same truck does not require a high bias while operating at high speeds on delivery or haul roads. This same reasoning also applies to many other types of equipment particularly construction equipment.
The obvious advantages of such high bias limited slip differentials are also accompanied by such disadvantages as increased tire wear; adversely affected steering; and overloaded wheel planetaries as well as axle shafts.